Summary of constraints on sterile neutrino dark matter in the plane of the sterile neutrino mass ﹩({{m}_{{\rm s}}})﹩ versus the mixing angle ﹩{{{\rm sin} }^{2}}(2\theta )﹩. The interpretation of the 3.5-keV x-ray line in terms of sterile neutrinos is shown in brown [64]. In the red regions sterile neutrinos are either under-abundant or overabundant [68]. The green region corresponds to the Tremaine–Gunn bound [69]. The pink region shows the constraint obtained from observations of the stellar velocity dispersion in the Fornax dwarf galaxy [70]. The rest of the regions are based on analysis of different celestial bodies using x-rays: Milky Way and Ursa Minor (dark blue) [71], Andromeda (M31) [72], Coma and Virgo clusters [73], cosmic x-ray background assuming Milky Way halo models (light blue, including hatching region [74]), Milky Way SPI-INTEGRAL exclusion [75], Milky Way HEAO-I exclusion [76], and the diffuse x-ray background [74].